Light responsive system



Oct. l, 1957 G. w. oNKsEN ETAL LIGHT RESPONSIVE SYSTEM Original Filed July 10, 1948 2 Sheets-Sheet l Gttornegs Oct. 1, 1957 e;I w. QNKSEN ET AL 2,808,539

LIGHT RESPONSIVE SYSTEM Original Filed July l0, 1948 2 Sheets-Sheet 2 United States LIGHT RESPQN SIV E SYSTEM George W. Gnksen and Charles W. Miller, Anderson, Ind., assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware Claims. (Cl. 315-83) The present invention relates to illumination systems and more particularly to light-sensitive electrical circuits adapted to control vehicle illumination systems in response to the intensity of illumination of a similar approaching system, and is a division of S. N. 37,984, tiled July 10, 1948, which issued May 25, 1954 as Patent No. 2,679,616.

The illumination systems of automotive vehicles are generally provided with dual filament headlamps with each filament in separately energizable electrical circuits controlled for alternate energization by the operator. The filaments are positioned with respect to the headlamp reflector to project a high and low beam of light declining to the longitudinal axis of the vehicle at different angles so that illumination patterns are cast at different distances in its path ahead. The high beam is generally preferred for night driving on rural highway-s which are not illuminated from other sources, Whereas the low beam is generally used for city driving conditions where additional illumination is provided.

To eliminate the hazards of passing due to the glare and dazzling elect of the high beam, the operator is required to manually operate a switch which lselectively energizes the low beam circuit. This operation may distract the operators attention from the path ahead and when the operator fails to depress the beam, extremely hazardous conditions prevail for the passing of oncoming operators.

It is therefore an object of the present invention to minimize the driving hazards prevalent under conditions of night driving by providing a light-sensitive electrical circuit for automatically controlling the illumination lsystem of Vvehicles in response to the intensity of illumination of a similar approaching system.

This and other objects are obtained in accordance with the present invention by providing a selective lightsen sitive electrical circuit for controlling vehicle headlight-V ing systems which is responsive to a predetermined light intensity to dim the system yet may be subjected to a wide variation of light intensity without aecting a deenergization of the dim circuit once it has been energized. A headlight system embodying the present invention comprises the conventional dual filament headlamps with independent electrical circuits for energizing one or the other, a light-sensitive electrical circuit including a photoelectric cell, a first and second stage of amplification, a relay for selectively energizing the independent filament circuits and a common source of electrical energy. The responsiveness to a predetermined light-intensity whilev remaining unaffected by wide variations of light intensities once the system has been `dimmed is obtained by including in the second stage of amplication, two amplier tubes of differing characteristics electrically connected in parallel.

Further objects and advantages of our invention will become apparent as the following description proceeds and the features of novelty which characterize our invention will be pointed out with particularity in the atent O claims annexed to and forming part of this spe'cication. For a better understanding of our invention reference I may be had to the accompanying drawings in which:

Figure 1 is a schematic diagram of the circuit utilizing the present invention for controlling a vehicle headlighting system;

Figure 2 is a schematic diagram illustrating one form of modification; and Y Figure 3 is a schematic diagram illustrating still another modification.

Referring now to Figure 1 of the drawings, there is illustrated a vehicle headlighting system embodying the present invention in which a pair of conventional headlamps, not shown, including high and low beam iilaments 2 and- 4 respectively, form part of electrical circuits energizable to provide either a manual or Aautomatic control of the system.

In the system, a conventional automotive vehicle storage battery 6 of the 6-volt type is provided as a source of electrical power. In this connection it will be understood that the battery -6 is a source of power for the ignition system of the vehicle 'as well as the lighting system. The negative terminal of battery 6 is connected to ground and the positive terminal is connected through conductor 8 to the movable arm 10 of a single pole, single throw master switch 12. The stationary contact 14 of yswitch 12 is connected through conductor 16, current limiting fuse 18 and conductor 20 to a terminal junction 22V. A branch conductor 24 connects terminal 22 with the movable arm 26 of a single pole, double throw electromagnetic relay switch 28 provided with loppositely disposed stationary contact terminals30 and 32. The movable arm 26 of swit-ch 28 is normally held in yield ing engagement with stationary contact terminal 32 which in turn is connected through conductor 34 to the low beam filaments 4 of the headlamps. The other sidesof the headlamp filaments 4 are grounded through a Iconductor 36. `T he circuit comprising contact 32, conductor 34, filaments 4 and conductor 36 form one branch of the headlamp circuit. The other branch comprises a conductor 38 which connects the high beam filaments 2 of the headlamps to contact 30 of the switch 28 and conductor 40 which connects the other sides of the iilaments 2 to ground.

To provide for the independent manual energization and de-energization of the headlamp circuits, the solenoid coil 42 of switch 28 forms part of a circuit which includes in series relationship a single pole, double throw, selector switch 44 and a singlepole, double throw foot selector switch 46. Terminal 22 Yis connected to the movable arm 48 of switch 44 through conductor 5t). The movable arm 48 is shown in a position to bridge two stationary contacts 52 and 54, both of which are connected in circuits to the automatic control and indicating means and will be described in detail hereinafter. An oppositely disposed contact 56 of switch 44 is connected through -conductor'58, terminal 60, conductor 62, terminal 64 and conductor 66 to a stationary contact68 of the foot` selector switch 46. The movable arm 70 of switch 46 is adapted to engage contact 68 and complete a circuit through conductor 72, Vsolenoid and conductor 74 to ground.

For automatic Ycontrol of ,the headlamp filaments a circuit is provided from the source 6 to the solenoid coil zationY and de-energization at substantially different current values. In thisJ circuit the stationary contact 52 of selector switch 44 Ais connected by a conductor 78 toa terminal junction which in turn is connected to the movable armV 82, ot relayswitch through conductor 34,'K

coil 42 of vswitch 28,

terminal junction 86 and conductor 88. The movable arm 82 cooperates with stationary contact 90 of relay switch 76 and is normally in yielding open circuit relationship. Contact 90 is connected through conductor 92, terminal junction 94 and conductor 96 to the remaining oppositely disposed stationary contact 98 of foot selector switch 46.

To reduce the destructive eiect of arcing between the movable arm 82 and the stationary contact 90 of relay switch 76, a shunt circuit including a 100 ohm resistor 100 Vand a .1 mfd. capacitor 102 is connected in series between the terminals 86 and 94. Y`

ln the headlighting system of the present invention the voltages suitable to the most ecient operation of the light responsive apparatus are provided by a conversion device 104 for changing the low Vvoltage direct current of the vehicle electrical system to a high voltage direct current suitable for the operation of the electronic elements in the circuit. Conversion devices such as the device employed in the system of the present invention are well known and are employed extensively to provide suitable voltages for the operation of vehicle radios. In

this connection the positive input terminal 106 of the' converter'is connected through conductor 108, terminal junction 110 and conductor 112 to the terminal 80. The negative terminal 114 is connected to ground by conductor 111. The lhigh voltage output terminal 116 is connected by a conductor 118, terminal junction 120, conductor 122, terminal junction 124 and conductor 126 to the solenoid coil 128 of the light responsive relay switch 76. The negative output terminal of the converter is connected within the converter to mound through terminal 114. The light responsive relay 76 has the other end of its solenoid coil 128 connected through conductor 130, terminal junction 132,V conductor 134, terminal junction 136, a 25,000 ohm resistor 138 land conductor 140 to the stationary contact 1420i a single pole, single throw, manual switch 144. The movable arm 145 of switch 144 is in yielding open circuit relation with contact 142 and is connected to ground by conductor 146. A shunt circuit is provided for the solenoid coil 128 of relay switch 76 which includes an 8 mfd. capacitor 143 connected between theV ends of the solenoid coil.

To provide the different voltages necessary to the operation of the various electronic elements in the light responsive apparatus a voltage divider network 147 comprising 4 sections of series-connected resistances 148, 150, 152 and 154 of 5.800 ohms, 3900 ohms, 800 ohms and 15,000 ohms respectively is connected between the high voltalge terminal 124 and ground. l The respective resistances are connected together inthe order enumerated by terminals 156, 158 and 160. l

A lilter 162 of 16 mfd. capacitance is connected across the output terminals 116 and 114 by means of conductor 118, terminal 120, conductor 168 and conductors 170 and 111, to minimize the ACripple voltage that is present in the output circuit of the converter 1 04.

As the Voltage at the Voutput terminals of the converter varies between about 260 and 420 volts due to the variation of the Vehicle systemvoltage between about 5.5 and 7 volts, voltage regulator means 164 -andv166 are connected in parallel with sections of the voltage divider network 147 to obtain stable Vvoltage levels of 150 and 75 volts respectively. The voltage regulator means 164 and 166 comprise a VR 150 yglow discharge tube which is connectedby conductors 172'and 174 between terminal 156 and ground, yand a. VR 75 glowrdischarge tube which is connected by conductors y176 and 178 between :terminal 160 andground. n

The electronic elements that comprise the light responsive apparatusV and provide for the energination and 'de'-Y energization of relay Vswitch76 include -a vphotocell 179 Vwhich controls apower amplifying" tube 190 hereinafter referred to as a first stage or primary amplier and a pair of power amplifying tubes 198 and 206 which are controlled `by the output of the primary amplifier and have their plates connected in panallel to the solenoid coil 128- of the 'relay switch 76. Tlhe pair of amplifying tubes 198 and 206 will be referred to hereinafter as the second stage or secondary amplifier. The photocell 179 is connected to the voltage divider 147 by a conductor 180 which connects its anode terminal to terminal 158 at the junction of the voltage divider resistance sections 150 and 152. By connecting the photocell anode to the voltage divider at this point, a voltage of about to 90 volts is provided for the operation of the cell at the most etlicient portion of its 'response curve. The cathode of the photocell is connected by conductor 181 to a terminal junction 182 which in turn is connected through a 500 megohm resistor 184 to ground 4and to the positive terminal of a one and one-fourth volt biasing battery 186 which lhas its negative terminal connected by a conductor 188 to the control grid of the multiple ygrid power amplifying tube 190 comprising the lrst stage or primary amplifier. The output or plate of tube 190 is connected by conductor 192, terminal junction 194 land conductor 196 to the control grid of the multiple grid power amplifying tube 198 comprising part of the second stage or secondary amplier and throulgh terminal 194, resistor 195, terminal junction 197, conductor 200, resistor 202 and conductor 204 to the control grid of the multiple grid power arnplifying tube 206 comprising the other part of the second stage or secondary amplifier. T'he resistors 195 and 202 have respective resistance values of 2 land 100 megohms. The plate of tube 190 is also connected by terminal 197 to terminal 160 of the voltage divider through an 8 megohm resistor 208, conductor 210, terminal junction 212 and conductor 214. A 70,000 ohm potentiometer 213 is connected between terminal 212,-and `ground and carries a sliding Contact 215 which is connected by a conductor 216 to the screen grid of first stage amplifying tube 190. Current :for heating the filament of tube 190 is supplied by connecting the lament of this tube to the -'volt battery circuit lat terminal 110. ln the circuit between the terminal and the filament there is connected in series a choke coil 218, lan automatic regulating ballastresistance 220, a junction terminal 222 and a 25 ohm resistor 224. Current is Ialso supplied from the battery to the iilament of tube 198 through. the choke coil 218 and ballast resistor 220 by connecting terminal 222 to the lament through conductor 226. The other sides of the lilaments of tube 190 and 198 are connected to ground. Y To obtain a stable voltage input of volts to the screen grids of tubes 198 and 206 of the secondary amplifier, they are connected in 4ser-ies'by conductors 228 and 230 to the 150 volt terminal 156 of the voltage divider 147. Voltagefor the cathodes of tubes 198 and 206 are supplied from the voltage divider 147, the cathode and suppressor grid of tube 198 being connected by conductor 232 to terminal 212 and the cathode and suppressor grid of tube 206 being connected by conductor 234 to the sliding-'contact 236 on the potentiometer section 154. The cathode of tube 206 is heated by an independent lament which has one side connected -by conductor 235 to the 6-volt battery source at the junction of conductor 88 and movable arm 82 of switch 76 and the other side connected to ground. The plates of the tubes 198 vand 206 are connected in parallel to the solenoid coil 128 of `rel-ay switchj, the plate of tube 206 being connected to terminal 132 through a 30,000 ohm resistorr133 and the plate of tube 198 being connected to terminal 136 by conductor 238. Y

VIndicating means for the light responsive'and manual control circuits are included in the switching circuit. These means' comprise indicator Vlamps 240 and 242. Lamp 240 has one side of its lament connected to terminal 60 by conductor 244 and the other side of the lament connectedto the contact 54 of switch 44 by conductor 246, junction terminal 248 and conductor 250. The filament of lamp 242 has one side connected to ground and the other side connected through a conductor 252 to the stationary contact 254 of an electromagnetic relay switch 156. The movable arm 255 of the relay switch 256 is in yielding closed circuit relationship with contact 254 and is connected by conductor 257, terminal junction 259 and conductor 261 to the terminal 248. The coil 263 of the relay 256 is energized through a circuit which connects one end of the coil through a conductor 265 to terminal 64 and the other end of coil to terminal 259.

In the circuit modification of the light responsive apparatus illustrated in Figure 2, the arrangement of the circuit and electronic elements is substantially the same as that of Figure 1 except that a duo diode tube 256 is connected between the multiple grid tube 190 of the primary amplifier and the multiple grid tube 206 of the secondary amplifier.

In this circuit the plate of the primary amplier tube 190 is connected to terminal 194 by conductor 192 with branch circuits connecting terminal 194 with the control grid of tube 198, one of the cathodes of tube 256 and the 75 volt terminal of the voltage divider 147. The circuit connecting the grid of tube 198 and the plate of tube 190 is the same as hereinabove described in connection with the circuit of Figure 1. The circuit to the 75 volt terminal of the voltage divider includes a l0 megohm resistor 260 connected between terminals 194 and 212 by con` ductors 25S and 262. A conductor 255 connects terminal 194 with the cathode of tube 256. The voltage of the control grid of tube 206 is controlled by the output plates of tube 256. These plates are connected in parallel circuits to a terminal junction 265 which is connected to the control grid of tube 206 by conductor 267. One plate of the diode is connected to terminal 265' through a 1% volt biasing battery 268 which has its positive terminal yconnected to the plate of tube 256 by conductor 269 and its negative terminal connected to terminal 265 by conductor 266. The other plate of tube 256 is connected to terminal 265 by conductor 264. The heater filaments of tube 256 are connected in series between ground and the conductor 235 by conductor 271. The remaining cathode of tube 256 is connected through a 2 megohm resistor 273 to the cathode of tube 206.

In the circuit modification of the light responsive apparatus illustrated in Figure 3 there is included a pair of multiple grid tubes 270 and 272 comprising a first stage or primary amplifier which have their outputs controlled by the photocell and which in turn control the outputsrof another pair of multiple grid tubes 274 and 276 comprising a second stage or secondary amplifier.

In this circuit arrangement the control grid of tube 272 is connected to the cathode of the photocell 179 through conductor 27S, terminal junction 280 and a 1% volt biasing battery 282 which is arranged with its negative termi- -nal connected to the control grid and the positive terminal connected to the terminal 280. A 100 megohm resistor 284 in series with a 500 megohm resistor 286 are connected between terminal 280 and ground. A conductor 28S connects the junction of resistors 284 and 286 to the control grid of tube 270. The plates of tubes 270 and 272 are connected respectively by conductors 290 and 292 to the control grids of tubes 274 and 276. Current is supplied to the filaments of tubes 270, 272 and 276 from the 6-volt battery circuit through terminal 110, choke coil 218 and ballast resistor 220 and the branch circuits comprising the conductors 294 and 296. The filaments of tubes 270 and 272 are connected in series circuit relationship between conductor 294 and ground by conductors 29S and 300 while the filament of tube 276 has one side connected to ground by conductor 302 and the other side connected to the conductor 296. Voltage is supplied to the screen grid of tube 272 by a circuit which connects one end of a 70,000 ohm potentiometer 304 to the volt terminal 160 of the voltage divider 147 and the other end of the resistor to ground. Resistor 304 is connected to terminal by a circuit which includes conductor 214, junction terminal 308, conductor 310, junction terminal 312, conductor 314, junction terminal 316 and conductor 318. A slidable contact 320 associated with the potentiometer 304 is connected by a conductor 322 to the screen grid of tube 272. Voltage is supplied to the screen grid of tube 270 by connecting the grid through conductor 324 to a slidable contact 236 which is associated with the potentiometer section 154 of the voltage divider 147. r1`he cathodes and suppressor grids of tubes 274 and 276 are connected respectively to terminals 308 and 316 by conductors 328 and 330; the suppressor grid of tube 274 being connected to the cathode externally by conductor 327. A 250,000 ohm resistor 332 and a 500,000 ohm resistor 334 are connected respectively between the plate of tube 270 and terminal 312 and the plate of tube 272 and terminal 316. Current is supplied to the filament of tube 274 by conductor 235 which is connected between the movable arm 82 of relay switch 76 and one side of the filament.

The other side of the filament of tube 274 is connected to ground by conductor 333. The plates of tubes 274 and 276 are connected respectively to terminals 132 and 136 in the coil circuit of relay switch '76 through a 100,000 ohm resistor 340 and conductor 342.

For the hereinabove described light responsive circuits to operate in response to predetermined light intensities to control the energization and de-energization of the headlamp filaments 2 and 4 through relay switch 76 it is first desirable to adjust the circuit to respond with predetermined current flow at the plate output of the tubes of the secondary amplifier. In this connection, switches 12 and 44 are closed to energize the current converter 104. The electronic elements which are connected to the high potential side of the converter are allowed to heat for a period of time so that they will operate efiiciently. The sliding contacts of three circuits are then adjusted to provide current fiow through coil 12S which will vary in accordance with the intensity of light of an approaching vehicle headlight system to cause de-energization of the coil when the approaching vehicle is at a predetermined distance ahead and energization of the coil when the approaching vehicle passes by.

To provide for the automatic control of the headlighting system, switch 10 is closed to energize the low beam filaments 4 through current fiow from the battery 6 through conductors 8, 16, 1S, 20 and 24, movable arm 26 and conductor 34. The movable arm 48 of switch 44 is then closed on contact 52 to energize the converter 104 through the circuit including conductors 7S, 112 and 103.

Referring now to the circuit `diagram :of Figure -l with the electronic elements sufiiciently heated and no light on the photocell 179, suiiicient `current liows in the circuit from terminal 116 of the converter through conductors 11S, 122, 126, coil 12S, conductors 130 and 134 to the plates of tubes 19S and 206 to cause energization of the relay `coil 123 and movement of arm 32 of relay switch 76 into engagement with contact 90. With the movable arm 70 of the foot switch 46 engaging contact 9S a circuit is completed to coil 42 from the battery through .convductors 8, 16, 20, 7S, S4, '86, 02, 96 .and 72. With coil 42 energized the movable arm 26 of relay switch 28 moves into engagement with contact 30 causinfy energization of the high beam filaments 2.

With the approach of a similar lighting system, light of gradually increasing intensity falls on the photocell 179 causing an increasing current flow from terminal 158 of the voltage divider through conductor 180, photocell 179, conductor 131 and resistor 184 to ground. With the gradually increasing current flow in this circuit the voltage at terminal 182 changes and gradually 'overcomes the negative grid bias on the control grid of tube caused by the biasing battery 186. As the bias onv the control Agrid gradually changes from negative toward -positive the flow of current from terminal 160 of the voltage divider through conductors 214, 210, resistors 208 and 195 and conductor 192 to the plate of tube 190 increase and a voltage drop occurs at terminals 197 and 194 due to the -IR drop across resistors 195 and 288,. These voltage changes are carried to the control grids of tubes 206 and 198 respectively through circuitsiincluding conductor 200, resistor 282 and conductor 284 and conductor 196 respectively. This causes .a change 4of grid bias on the control tubes 198 and 2116 causing both tubes to become sequentially n-onconducting; tube 198 being the rst to cut oft but relay 128 will not drop out until tube 206 is cut down in conductance to a low value after tube 198 is nonconducting. With very little or no current owing to the plates of tubes 296 and 198 the coil 128 of relay 76 is de-ener-gized moving arm 82 out 1of engagement with contact 9).and the circuit through coil 42 of relay 28 is broken causing the movable arm 26 to move into engagement with contact 32 for the energization of low beam laments 4 and the de-energization of high beam lilaments 2.

-If the source of illumination to which the photocell is exposed then begins to decrease in intensity, a current of decreasing value flows from the terminal 158 of the voltage divider through the circuit including the photocell to ground as hereinabove mentioned. Accordingly, the voltage at terminal 182 decreases until the voltage of the biasing battery is imposed on the control grid of tube 190. The flow of current through tube 196 decreases and lconsequently the voltages at terminals 197 and 194 increase altering the grid 'bias in tubes 206 and 198. As these biasing voltages change the tiow of current in tube 206 gradually increases to normal value, and tube 198 begins to approach the conducting point. However, while tube 198 remains nonconductive there isV insuiicient current flow in the coil circuit of relay 76 to cause it to move the arm 82 into engagement with contact 9G. When it ydoes become conductive sucient current ows in the relay circuit to cause relay 76 t-o move the arm S2 into engagement with Contact 90 and tilaments 2 and 4 of the headlamp circuit respectively are energized and de-'energized There is thus a denite difference in the illumination level at relay drop-out to that at relay return. With this arrangement it will be obvious that substantial changes in intensity of illumination are required before the relay 7 6 will be energized or tie-energized from its existing state thereby preventing iiickering or repeated alternate energization of the filaments due to extraneous lighting conditions.

It the operator of the vehicle should desire to reenergize the high beam elements 2 while the low beam elements are energized and under the `control of the light-responsive apparatus, the independent resetting manual foot switch 144 is provided to close a cir-cuit through the coil 128 of relay 76 from the terminal 116 of the converter 104 to ground. This circuit comprises conductors 118, 122, 126, relay coil 128, conductors 130, 134, resistor 138, conductor 149, switch 144 and conductor 146.

Manual control of the laments 2 `and 4 is obtained in the same manner as in the conventional headlight system. In this connection the movable arm 48 of selector switch 44 is moved into engagement with contact 56 thereby completing a circuit from battery 6 through conductors 8, 16, 20, 50, 58, 62 and 66 to the stationary contact 68 of the foot switch 46. When the movable arm 7B moves into enga-gement with contact 68, the circuit is completed from the battery 6 to the coil of relay 28 through the switch 46 and conductor 72. Movable arm 26 of relay `switch 2S moves into engagement with contact 36 and the high beam il-aments 2 are energized. Manually :breaking lthe circuit at switch 46 causes a deenergization of relay coil 42 and an energization of the circuit to the low beam filaments 4. Y

Lamps 240 and 242 indicate the`controlling condition ofthel light responsive apparatus and the respective energization of the headlamp ilaments. With the movable arm 48 of switch 44 in engagement with contacts 52 and 54 4for energization of the light responsive :apparatus Vas hereinabove described,V a circuit is completed from terminal 248v through conductor 246, lamp 240 and conductor 244 to terminal 68. An additional circuit is completed from terminal 248 through conductor 261, coil 263 of relay switch 256 and conductor 265 to terminal This circuit also includes a branch `circuit from conductor 261 to the movable arm 255 through conductor 257. With the coil of relay switch 256 cie-energized, this circuit is completed through contact 254, conductor 252 Vand lamp-242 to ground. When the arm 70 of switch 46 in engagement with contact 98 for control of the llaments 2 and 4 by the light responsive apparatus, lamp 242 is energized, indicating that the light responsive apparatus is controlling. When the movable arm 7i) of switch 46 moves into engagementV with contact 68, coil 263 of relay 256 i-s energized moving arm 255 out of engagement with contact 254 whereby the lamp 242 is de-energized. At the same time, lamp 240 becomes energized. With switch arm 48 moved lout of engagement with contact 54 both indicating lamps become de-energized. With such an arrangement of indicating lamps there is visual means for indicating which of the headlamp filaments is energized when they are controlled manually and Whether the filaments are under the control of the light responsive apparatus.

The operation of the light responsive circuit of Figure 2 is substantially the same as that of Figure l. In this circuit, the intensity of light on the photocell determines the current ow in tube and through resistor 266 which in turn controls the current iiow in tubes 198 and 206 by changing the voltage on the control grids of these tubes. With no light on the photocell, both tubes 198 and 206 conduct suihcient current to cause the energization of coil 128 of relay 76 at a substantially high current value. As the photocell 'becomes exposed to increasing intensities of light, the voltage bias on the control grids of tubes 198 and 206 causes the tube 198 to become nonconductive 'and reduces the current ilow of tube 206 to a sutliciently low current ow to cause relay coil 128 to become de-energized. Current value at which the relay coil becomes de-energized is substantially less than that at which it becomes energized. In this circuit the purpose of the diode tube 256 is to replace resistor 202 of the circuit of Figure l and prevent t'he control grid of tube 206 -from becoming positive with respect to the cathode.

In the light responsive circuit of Figure 3 the operation is substantially the same as that of light responsive circuits of Figures l and 2 except that the flow of current through tubes 274 and 276 is directly and separately controlled by tubes 27 0 and 272 respectively of the primary amplifier. These tubes of the primary ampliiier are in turn controlled by the photocell. As in the light responsive circuits of Figures l and 2 when the photocell is not exposed to light tubes 274 and 276 both conduct current of substantially high value to energize relay coil 128. As the intensity of light on the photocell increases the photocell conducts increasingly more current in the circuit from the voltage divider to ground through the photocell, conductor 278 and resistors 284 and 286. With increasing current'in this circuit voltage changes occur across resistors 284 and 28,6 to cause the voltage bias on the control grids of tubes 276 and 272 to change, thus changing the current output of the tubes 274- and 276 and the voltage bias on the control grids of tubes 274 and 276. With suficient light intensity on the photocell, tube 276 no longer conducts current and tube 274 conducts current of less value than that required to retain relay coil 128 energized. While specic circuit constants have been used in connection with the description of the circuitsV of the present invention and their operation it will be understood by those skilled in the art that they are illustrative and that the circuits are capable of operation at other values than those recited.

With the light responsive circuits such as described above wherein the light responsive relay controlling the headlamp filament circuit is in turn controlled by an amplifier comprising two amplifier tubes in parallel, the energizing and de-energizing of the headlamp filaments is accomplished at substantially different intensities of illumination. This important feature makes the operation of an automatic dimmer device for vehicle headlighting systems feasible because of the lack of response of the device to other sources of light causing ickerin-g due to the repeated energization and de-energization of the high and low beam headlamp filaments.

We claim:

l. In a light controlled system for multi-filament headlamps, a source of electrical power, switching means connected to the source and to-the filaments to alternately connect the filaments to the source, light actuated control means connected to and operating the switching means dependent upon the amount of incident light, manual means also connected to and operating the switching means to switch filaments, and a plurality of indicating means connected to the source of power, to the light control and to the manual means to indicate operating conditions.

2. In a control system for multi-filament lamps, a source of electrical power, switching means interconnecting said source and filaments to alternately energize different filaments, magnetic means to actuate said switching means, a light sensitive control system connected to the magnetic means and to the source of power to control the same dependent upon incident light, manual switching means connected to the magnetic means to independently control actuation of the switching means, and indicating means connected to said source and said magnetic means to indicate the condition of the control system.

3. In a control system for multi-filament lamps, a

source of electrical power, switching means interconnectingsaid source and filaments to alternately energize different filaments, magnetic means to actuate said switching means, a light sensitive control system connected to the magnetic means and to the source of power to control the same dependent upon incident light, manual switching means connected to the magnetic means to control actuation of the switching means, a master switch connected to said source of power and to the light sensitive system and the manual switching means to determine which shall control, and indicating means connected to said master switching means to indicate which system of control is active.

4. In a control system for multi-filament lamps, a source of electrical power, switching means interconnecting said source and filaments to alternately energize different filaments, magnetic means to actuate said switching means, a light sensitive control system connected to the magnetic means and to the source of power to control the same dependent upon incident light, manual switching means connected between the light sensitive system and the magnetic means and to the source of power, master switching means connected between said source of power and the light sensitive system and between the source and the manual switching means to control the type of operation, and indicating means connected to the master switching means to indicate the type of operation.

5. In a control system for multi-filament lamps, a source of electrical power, switching means interconnecting said source and commonly to one filament in each lamp to alternately energize one set of filaments or the other, energizable means to operate the switching means, light controlled switching means connected to the source of electrical power and to the energizable means to control the switching means, manual switching means connected between the light controlled switching means and the energizable means and to the source of electrical power to alternately connect the light controlled switching means or the source of power to the energizable means to operate the switching means and indicating means connected to the manual switching means and to the source of electrical power to indicate which set of filaments are energized and whether the automatic control is or is not controlling.

References Cited in the le of this patent UNITED STATES PATENTS 1,935,698 Decker et al Nov. 2l, 1933 2,240,843 Gillespie May 6, 1941 2,558,969 Le Croy July 3, 1951 

